This impressive Cortinarius is mycorrhizal with birch, and is a common late summer and fall mushroom in northern forests where birch appears. Its stem has a swollen base, its dry cap is yellow-brown to reddish brown, and its gills are dirty yellowish to pale cinnamon before maturity. The most distinctive feature of Cortinarius armillatus, however, is the series of two to four bright, orange-red "bracelets" encircling the stem.

A recent investigation of about 1,000 armillatus-like specimens from northern Europe (Niskanen and collaborators, 2011) found support for six separate species, three of which are known to occur in North America: Cortinarius armillatus, Cortinarius luteo-ornatus, and Cortinarius paragaudis. Among these, Cortinarius armillatus is distinct by virtue of its bright orange-red (as opposed to pinkish or wine red) bracelets; its comparatively long, ellipsoid, thick-walled spores; and its exclusive association with birch, rather than conifers. That last item, however, can be very tricky to assess in northern forests, which are often "mixed."